- ID:
- ivo://CDS.VizieR/J/MNRAS/434/1411
- Title:
- Variability of broad emission lines in QSOs
- Short Name:
- J/MNRAS/434/1411
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the variability of the high-ionization Ly{alpha} {lambda}1216 broad emission line (BEL) in a sample of 61 high-luminosity, high-redshift quasars observed at two epochs by the Sloan Digital Sky Survey. These bright objects lie in the redshift interval z=[2.5, 4.3] and have luminosities 3.4x10^45^<~{lambda}*L_{lambda}_<~3.4x10^46^erg/s at 1450{AA}. Utilizing improved spectrophotometric flux calibrations relative to nearby compact stars observed simultaneously, we are able to measure the flux changes in Ly{alpha} and the nearby continuum at two epochs. We find 20 objects that exhibit Ly{alpha} BEL flux variability at a significance level greater than 5{sigma} on time-scales ranging from days to years in the quasar rest frame.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/461/183
- Title:
- Variability of classical T Tauri
- Short Name:
- J/A+A/461/183
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of a study the long term variability of Classical T Tauri stars (CTTS) over up to 20 years, characterize it from a set of statistical parameters and discuss its origin. We characterize the long term photometric variations of 49 CTTs with sufficient data for allowing a robust statistical analysis and propose an empirical classification scheme. Several patterns of long term photometric variability are identified. The most common pattern, exhibited by a group of 15 stars which includes T Tau itself, consists of low level variability (with V-amplitude less than 0.4mag) with no significant changes occurring from season to season over many years. A related subgroup of 22 stars exhibit a similar stable long term variability pattern, though with larger amplitudes (up to 1.6mag). Besides these representative groups, we identify three smaller groups of 3-5 stars each of which have distinctive photometric properties. The long term variability of most CTTS is fairly stable and merely reflects shorter term variability due to cold and hot surface spots. Only a small fraction of CTTS undergo significant brightness changes on the long term (months, years), which probably arise from slowly varying circumstellar extinction.
20413. Variability of CP stars
- ID:
- ivo://CDS.VizieR/J/A+AS/105/125
- Title:
- Variability of CP stars
- Short Name:
- J/A+AS/105/125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/AZh/78/408
- Title:
- Variability of Cyg X-1 in 1994-1998
- Short Name:
- J/AZh/78/408
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photoelectric UBVR photometry of Cyg X-1 obtained during the coordinated international campaign 'Optical Monitoring of Unique Astrophysical objects', carried out in observatories of CIS countries (Georgia, Kazakhstan, Russia, Uzbekistanin and Ukraine) 1994-1998 is presented. The data are presented as a single set, taking into account systematic differences between individual data sets. In total 2258 UBVR observations were obtained during 407 nights.
- ID:
- ivo://CDS.VizieR/J/PAZh/26/27
- Title:
- Variability of Cyg X-1 (V1357) in 1995-1996
- Short Name:
- J/PAZh/26/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photoelectric UBVR photometry of Cyg X-1 with 1-m Tian'-Shan' and 48-cm Maidanak Observatory reflectors from October 1995 through November 1996 are presented.
- ID:
- ivo://CDS.VizieR/J/A+A/553/A107
- Title:
- Variability of 198 extragalactic radio sources
- Short Name:
- J/A+A/553/A107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Combining measurements taken using the Wilkinson Microwave Anisotropy Probe (WMAP) from 2001 to 2008 with measurements taken using Planck from 2009 to 2010, we investigate the long-term flux density variability of extragalactic radio sources selected from the Planck Early Release Compact Source Catalogue. The single-year, single-frequency WMAP maps are used to estimate yearly-averaged flux densities of the sources in the four WMAP bands: Ka (33GHz), Q (41GHz), V (61GHz), and W (94GHz). We identify 82, 67, 32, and 15 sources respectively as variable at greater than 99% confidence level in these four bands. The amplitudes of variation are comparable between bands, and are not correlated with either the flux densities or the spectral indices of the sources. The number counts of WMAP Ka-band sources are stable from year to year despite the fluctuation caused by individual source variability. Most of our sources show strong correlation in variability between bands. Almost all the sources that show variability are blazars. We have attempted to fit two simple, four-parameter models to the time-series of 32 sources showing correlated variability at multiple frequencies - a long-term flaring model and a rotating-jet model. We find that 19 sources (60%) can be fit with the simple rotating-jet model, and ten of these also fit the simple long-term flaring model. The remaining 13 sources (40%) show more complex variability behaviour that is not consistent with either model. Extended radio galaxies in our sample show no sign of variability, as expected, with the exception of Pictor A for which we report evidence for a millimetre flare lasting between 2002 and 2010.
- ID:
- ivo://CDS.VizieR/J/MNRAS/415/1061
- Title:
- Variability of FBS blue stellar objects
- Short Name:
- J/MNRAS/415/1061
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new method for combined calculations of magnitudes based on accurate measurements of POSS1 and POSS2 epoch plates is given. The photometric accuracy of various surveys and catalogs has been estimated and established and statistical weights for each of them have been calculated. To achieve the best possible magnitudes, weighted averaging of data from USNO-A2.0, APM, MAPS, USNO-B1.0, and GSC 2.3.2 catalogs have been used. The rms accuracy of magnitudes achieved for POSS1 is 0.184 mag for B and 0.173 mag for R and for POSS2 is 0.138 mag for B and 0.128 mag for R. We have derived the best POSS1 and POSS2 magnitudes for the FBS blue stellar objects. We have refined the transformation formulae between the POSS1 and POSS2 magnitudes and SDSS ones and standard UBV system. Using these accurate magnitudes, we have estimated the variability of the FBS blue stellar objects and revealed probable and possible variables. We have worked out methods to control and exclude accidental errors that appear in any survey. We have compared and combined our results with those given in NSVS database and obtained better candidates for variability. Having excluded variables, we have combined POSS1 and POSS2 data for the rest of objects to achieve even better magnitudes and colors; the rms being smaller than 0.1 mag both in B and R and for the B-R colors. This approach has been applied to the First Byurakan Survey blue stellar objects containing significant number of white dwarfs, cataclysmic variables, as well as extragalactic objects (quasars, Seyferts, BL Lac objects). Altogether 336 variable objects have been revealed with POSS2-POSS1 >= 3{sigma} of the errors. An electronic table of these objects is given. Candidate variables are divided into 4 classes: extreme, strong, probable and possible variables. For a more reliable sample of variable objects we excluded possible ones from the list and were left with 161 objects. Analyzing radio and X-ray properties of these objects, we have revealed their nature and re-discovered or revealed candidate AGN, CVs, WDs and other objects.
- ID:
- ivo://CDS.VizieR/J/A+A/370/468
- Title:
- Variability of gamma-ray sources
- Short Name:
- J/A+A/370/468
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of 40 low-latitude unidentified 3EG gamma-ray sources which were found to be not positionally coincident with any known class of potential gamma-ray emitters in the Galaxy (Romero et al., 1999A&A...348..868R). We have performed a variability analysis which reveals that many of these 40 sources are variable. These sources have, in addition, a steep mean value of the gamma-ray spectral index, <{Gamma}>=2.41+/-0.2, which, combined with the high level of variability, seems to rule out a pulsar origin. The positional coincidences with uncatalogued candidates to supernova remnants were also studied. Only 7 sources in the sample are spatially coincident with these candidates, a result that is shown to be consistent with the expected level of pure chance association. A complementary search for weak radio counterparts was also conducted and the results are presented as an extensive table containing all significant point-like radio sources within the 40 EGRET fields. We argue that in order to produce the high variability, steep gamma-ray spectra, and absence of strong radio counterparts observed in some of the gamma-ray sources of our sample, a new class of objects should be postulated, and we analyze a viable candidate.
- ID:
- ivo://CDS.VizieR/J/A+A/455/L1
- Title:
- Variability of 5 gravitationally lensed QSOs
- Short Name:
- J/A+A/455/L1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have searched for microlensing variability in the light curves of five gravitationally lensed quasars with well-determined time delays: SBS 1520+530, FBQ 0951+2635, RX J0911+0551, B1600+434 and HE 2149-2745. By comparing the light curve of the leading image with a suitably time offset light curve of a trailing image we find that two (SBS 1520+530 and FBQ 0951+2635) out of the five quasars have significant long-term (~ years) and short-term (~100-days) brightness variations that may be attributed to microlensing. The short-term variations may be due to nanolenses 10^-4^-10^-3^M_{sun}_, relativistic hot or cold spots in the quasar accretion disks, or coherent microlensing at large optical depth.
- ID:
- ivo://CDS.VizieR/J/ApJ/660/1486
- Title:
- Variability of LMC semiregular variables
- Short Name:
- J/ApJ/660/1486
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observational arguments supporting the binary explanation of the long secondary period (LSP) phenomenon in red giants are presented. Photometry of about 1200 semiregular variables with LSPs in the Large Magellanic Cloud is analyzed using the MACHO and OGLE photometry. For about 5% of these objects, additional ellipsoidal-like or eclipsing-like modulation with the same periods as the LSP is detectable. These double-humped variations are usually shifted in phase compared to LSP light curves. I discuss the model of a binary system with a red giant as the primary component and a low-mass object as the secondary. The mass lost by the red giant through the wind follows a spiral pattern in the orbit around the primary star and obscures it, causing LSP variations.
